linux-kernel - Re: [patch 5/7 -mm] oom: replace sysctls with quick mode

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Message-ID: <alpine.DEB.2.00.1002120150380.22883@chino.kir.corp.google.com>
Date:	Fri, 12 Feb 2010 01:58:10 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Lubos Lunak <l.lunak@...e.cz>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch 5/7 -mm] oom: replace sysctls with quick mode

On Fri, 12 Feb 2010, KAMEZAWA Hiroyuki wrote:

> > Two VM sysctls, oom dump_tasks and oom_kill_allocating_task, were
> > implemented for very large systems to avoid excessively long tasklist
> > scans.  The former suppresses helpful diagnostic messages that are
> > emitted for each thread group leader that are candidates for oom kill
> > including their pid, uid, vm size, rss, oom_adj value, and name; this
> > information is very helpful to users in understanding why a particular
> > task was chosen for kill over others.  The latter simply kills current,
> > the task triggering the oom condition, instead of iterating through the
> > tasklist looking for the worst offender.
> > 
> > Both of these sysctls are combined into one for use on the aforementioned
> > large systems: oom_kill_quick.  This disables the now-default
> > oom_dump_tasks and kills current whenever the oom killer is called.
> > 
> > The oom killer rewrite is the perfect opportunity to combine both sysctls
> > into one instead of carrying around the others for years to come for
> > nothing else than legacy purposes.
> > 
> > Signed-off-by: David Rientjes <rientjes@...gle.com>
> 
> seems reasonable..but how old these APIs are ? Replacement is ok ?
> 

I'm not concerned about /proc/sys/vm/oom_dump_tasks because it was 
disabled by default and is now enabled by default (unless the user sets 
this new /proc/sys/vm/oom_kill_quick).  So existing users of 
oom_dump_tasks will just have their write fail but identical behavior as 
before.

/proc/sys/vm/oom_kill_allocating_task is different since it now requires 
enabling /proc/sys/vm/oom_kill_quick, but I think there are such few users 
(SGI originally requested it a couple years ago when we started scanning 
the tasklist for CONSTRAINT_CPUSET in 2.6.24) and the side-effect of not 
enabling it is minimal, it's just a long delay at oom kill time because 
they must scan the tasklist.  Therefore, I don't see it as a major problem 
that will cause large disruptions, instead I see it as a great opportunity 
to get rid of one more sysctl without taking away functionality.

> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 

Thanks!
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